The present invention relates generally to cooling holes in gas turbine engine components, and more particularly to cooling holes adapted for producing turbulent flow, commonly referred to as xe2x80x9cturbulatedxe2x80x9d cooling holes by gas turbine engine designers.
Cooling holes are formed in gas turbine engine components such as vanes, blades and shrouds for transporting film cooling air through the component to cool the component and to form a thermal barrier between the component and hot gases traveling through a main flow path of the engine. As a result of film cooling, the component experiences a cooler temperature than it would otherwise. Accordingly, film cooling permits engine control changes to increase flow path temperatures without adversely affecting the components because the flow path temperatures can be increased until the surface temperatures of the components reach the same level as they would be without film cooling. Alternatively, the flow path temperatures can be kept the same and the component temperatures can be decreased, resulting in increased component life.
Typically, the film cooling air forms a boundary layer which flows along the surface of the component downstream from the hole. This boundary layer physically separates the flow path gases from the component and creates the thermal barrier between the flow path gases and the component. Frequently, the boundary layer has laminar flow characteristics for some distance downstream from the holes. However, laminar flow does not produce as effective a thermal barrier as turbulent flow. Thus, it is desirable to create a boundary layer having turbulent flow. One way to create turbulent flow is to separate the boundary layer from the component by providing a discontinuity along the surface of the component. Prior attempts to create turbulent flow by using cooling holes having diameters less than 0.010 inches have been unsuccessful because the methods could not create repeatable discontinuities inside these small holes.
Briefly, apparatus of this invention is a component for use in a flow path of a gas turbine engine. The component includes a body having an exterior surface mountable in the gas turbine engine so the exterior surface is exposed to gases flowing through the flow path of the engine. The body has a cooling hole extending through the body to the exterior surface for transporting cooling air from a cooling air source outside the flow path of the engine to the exterior surface of the body for providing a layer of cooling air adjacent the exterior surface of the body to cool the surface and create a thermal barrier between the exterior surface and the gases flowing through the flow path of the gas turbine engine. The cooling hole is defined by an elongate annular surface extending through the body of the component and terminating at the exterior surface of the body. The hole has a length, a maximum width of less than about 0.010 inches, and a cross-sectional shape which varies along the length in a predetermined manner for affecting characteristics of cooling air transported through the hole.
In another aspect, the invention includes a method of forming a turbulated cooling hole in a component for use in a gas turbine engine. The component includes a body having an exterior surface mountable in the gas turbine engine so the exterior surface is exposed to gases flowing through the flow path of the engine. The method comprises the step of forming a hole in the body of the component. The hole is defined by an elongate annular surface extending through the body of the component and terminating at the exterior surface of the body. A mandrel is positioned in the hole formed in the component. The mandrel has a length and a cross-sectional shape which varies along the length in a predetermined manner. Further, the method includes the steps of permanently deforming the body toward the mandrel to reduce a distance between the elongate annular surface defining the hole and the mandrel and removing the mandrel from the hole of the deformed component thereby to provide a turbulated hole having a cross section which varies along a length of the annular surface defining the hole.